Earlier quoted context omitted.
You know you turn that DNS server off by adding "DNSStubListener=no" to /etc/systemd/resolved.conf right?
Then.. why does it exist? More importantly, why is it enabled by default? Does systemd want to be an init system? A logging system? a dnsmasq replacement?
Folks at Red Hat noticed that the Linux userland architecture is not convenient for what they would like to build. So they are building systems which replace the traditional mechanisms: first DBus, then systemd, which is an umbrella of many services: init + service monitoring + containers, logging, interactive login, some networking, etc. I suppose that in 10 years a linux kernel + systemd could be a complete system, with little need for other userland.